1. Field of the Invention
The present invention relates to a process for producing a vibration isolator which can be appropriately used as suspension arms, engine mounts, etc., for automobiles, for example.
2. Description of the Related Art
Conventionally, a suspension bushing has been known as an insulator-and-connector device which is used at a connecting portion of a suspension arm for an automobile, for instance. As illustrated in FIG. 7, the bushing comprises a pipe-shaped inner cylindrical fitting 101, an outer cylindrical fitting 102, and a substantially-cylinder-shaped rubber elastic member 103. The outer cylindrical fitting 102 is disposed outside the inner cylindrical fitting 101 away therefrom by a predetermined distance and substantially coaxially therewith. The rubber elastic member 103 is bonded by vulcanization to an outer peripheral surface of the inner cylindrical fitting 101 and to an inner peripheral surface of the outer cylindrical fitting 102.
Taking the characteristics and durability of the rubber elastic member 103 into consideration, the bushing is subjected to a drawing process so that it is compressed and deformed inward in radial direction as illustrated in FIG. 8. Thereafter, as illustrated in FIG. 9, the bushing is fitted with and fastened to a suspension arm 104 by pressing the outer cylindrical fitting 102 into an installation hole 141 which is disposed at one end of the suspension arm 104. Then, the other installation axis, such as a connecting arm, etc., is fitted with and fastened to an inner hole of the cylindrical inner fitting 101 by fastening a bolt, or the like. Thus, the conventional bushing is put into service.
In the conventional bushing, the outside-diameter dimension of the outer cylindrical fitting 102 is required to exhibit a high accuracy because the outer cylindrical fitting 102 is fitted with and fastened to the installation hole 141 of the suspension arm 104 by pressing. However, it is difficult for the outer cylindrical fitting 102, which has been subjected to the drawing process before the pressing operation, to exhibit a satisfactory dimensional accuracy. When the outer cylindrical fitting 102 is used as it is after it has been subjected to the drawing process, it is difficult to sufficiently and stably secure the efficiency of the press-in operation and the fastening strength after the press-in operation.
For example, when the outside-diameter dimension of the outer cylindrical fitting 102 is much larger than the inside-diameter dimension of the installation hole 141 entirely in peripheral direction or partially, the galling arises during the press-in operation so that it is extremely difficult to press the outer cylindrical fitting 102 into the installation hole 141. On the other hand, when the outside-diameter dimension of the outer cylindrical fitting 102 is much smaller than the inside-diameter dimension of the installation hole 141 entirely in peripheral direction or partially, it is difficult to sufficiently secure the fastening strength after the press-in operation.
Hence, in order to secure the required dimensional accuracy, the outer cylindrical fitting 102 has been conventionally further subjected to a grinding process, and the like, after it is subjected to the drawing process. Since these special operations require special manufacturing processes and facilities, there arise problems in that the manufacture is accordingly cumbersome and results in a sharply increased manufacturing cost.